buffer_view.hpp

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// Copyright 2024 Man Group Operations Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#pragma once
 
#include "sparrow/buffer/buffer.hpp"
#include "sparrow/utils/contracts.hpp"
 
namespace sparrow
{
    /*
     * Non-owning view of a contiguous sequence of objects of type T.
     *
     * Although this class looks very similar to std::span, it provides
     * methods that are missing in C++20 std::span (like cbegin / cend),
     * and additional std::vector-like APIs.
     */
    template <class T>
    class buffer_view
    {
    public:
 
        using self_type = buffer_view<T>;
        using value_type = T;
        using reference = T&;
        using const_reference = const T&;
        using pointer = T*;
        using const_pointer = const T*;
        using size_type = std::size_t;
        using difference_type = std::ptrdiff_t;
 
        using is_buffer_view = std::true_type;
 
        using iterator = pointer_iterator<pointer>;
        using const_iterator = pointer_iterator<const_pointer>;
        using reverse_iterator = std::reverse_iterator<iterator>;
        using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
        constexpr buffer_view() = default;
        constexpr explicit buffer_view(buffer<T>& buffer)
            requires(!std::is_const_v<T>);
        template <class U>
            requires std::same_as<std::remove_const_t<T>, U>
        constexpr explicit buffer_view(const buffer<U>& buffer);
        constexpr buffer_view(pointer p, size_type n);
 
        template <class It, class End>
            requires std::contiguous_iterator<It> && std::sentinel_for<End, It>
                     && std::same_as<std::remove_const_t<std::iter_value_t<It>>, std::remove_const_t<T>>
        constexpr buffer_view(It first, End last);
 
        [[nodiscard]] constexpr bool empty() const noexcept;
        [[nodiscard]] constexpr size_type size() const noexcept;
        [[nodiscard]] constexpr size_type max_size() const noexcept;
 
        constexpr reference operator[](size_type);
        constexpr const_reference operator[](size_type) const;
 
        constexpr reference front();
        constexpr const_reference front() const;
 
        constexpr reference back();
        constexpr const_reference back() const;
 
        template <class U = T>
        constexpr U* data() noexcept;
 
        template <class U = T>
        constexpr const U* data() const noexcept;
 
        constexpr iterator begin();
        constexpr iterator end();
 
        constexpr const_iterator begin() const;
        constexpr const_iterator end() const;
        constexpr const_iterator cbegin() const;
        constexpr const_iterator cend() const;
 
        constexpr reverse_iterator rbegin();
        constexpr reverse_iterator rend();
 
        constexpr const_reverse_iterator rbegin() const;
        constexpr const_reverse_iterator rend() const;
        constexpr const_reverse_iterator crbegin() const;
        constexpr const_reverse_iterator crend() const;
 
        constexpr void swap(buffer_view& rhs) noexcept;
 
        constexpr buffer_view subrange(size_type pos, size_type count) const;
        constexpr buffer_view subrange(size_type pos) const;
        constexpr buffer_view subrange(const_iterator first, const_iterator last) const;
 
        constexpr operator buffer<std::remove_const_t<T>>() const;
 
    private:
 
        pointer p_data = nullptr;
        size_type m_size = 0u;
    };
 
    template <class T>
    bool operator==(const buffer_view<T>& lhs, const buffer_view<T>& rhs);
 
    /******************************
     * buffer_view implementation *
     ******************************/
 
    template <class T>
    constexpr buffer_view<T>::buffer_view(buffer<T>& buffer)
        requires(!std::is_const_v<T>)
        : p_data(buffer.data())
        , m_size(buffer.size())
    {
    }
 
    template <class T>
    template <class U>
        requires std::same_as<std::remove_const_t<T>, U>
    constexpr buffer_view<T>::buffer_view(const buffer<U>& buffer)
        : p_data(buffer.data())
        , m_size(buffer.size())
    {
    }
 
    template <class T>
    constexpr buffer_view<T>::buffer_view(pointer p, size_type n)
        : p_data(p)
        , m_size(n)
    {
        SPARROW_ASSERT_TRUE(p != nullptr || n == 0u);
    }
 
    template <class T>
    template <class It, class End>
        requires std::contiguous_iterator<It> && std::sentinel_for<End, It>
                     && std::same_as<std::remove_const_t<std::iter_value_t<It>>, std::remove_const_t<T>>
    constexpr buffer_view<T>::buffer_view(It first, End last)
        : p_data(std::to_address(first))
        , m_size(static_cast<size_type>(std::distance(first, last)))
    {
        SPARROW_ASSERT_TRUE(first <= last);
    }
 
    template <class T>
    constexpr bool buffer_view<T>::empty() const noexcept
    {
        return size() == size_type(0);
    }
 
    template <class T>
    constexpr auto buffer_view<T>::size() const noexcept -> size_type
    {
        return m_size;
    }
 
    template <class T>
    constexpr auto buffer_view<T>::max_size() const noexcept -> size_type
    {
        return size();
    }
 
    template <class T>
    constexpr auto buffer_view<T>::operator[](size_type pos) -> reference
    {
        SPARROW_ASSERT_TRUE(pos < size());
        return data()[pos];
    }
 
    template <class T>
    constexpr auto buffer_view<T>::operator[](size_type pos) const -> const_reference
    {
        SPARROW_ASSERT_TRUE(pos < size());
        return data()[pos];
    }
 
    template <class T>
    constexpr auto buffer_view<T>::front() -> reference
    {
        SPARROW_ASSERT_TRUE(!empty());
        return data()[0];
    }
 
    template <class T>
    constexpr auto buffer_view<T>::front() const -> const_reference
    {
        SPARROW_ASSERT_TRUE(!empty());
        return data()[0];
    }
 
    template <class T>
    constexpr auto buffer_view<T>::back() -> reference
    {
        SPARROW_ASSERT_TRUE(!empty());
        return data()[m_size - 1];
    }
 
    template <class T>
    constexpr auto buffer_view<T>::back() const -> const_reference
    {
        SPARROW_ASSERT_TRUE(!empty());
        return data()[m_size - 1];
    }
 
    template <class T>
    template <class U>
    constexpr U* buffer_view<T>::data() noexcept
    {
#if defined(__GNUC__)
#    pragma GCC diagnostic push
#    pragma GCC diagnostic ignored "-Wcast-align"
#endif
        return reinterpret_cast<U*>(p_data);
#if defined(__GNUC__)
#    pragma GCC diagnostic pop
#endif
    }
 
    template <class T>
    template <class U>
    constexpr const U* buffer_view<T>::data() const noexcept
    {
#if defined(__GNUC__)
#    pragma GCC diagnostic push
#    pragma GCC diagnostic ignored "-Wcast-align"
#endif
        return reinterpret_cast<const U*>(p_data);
#if defined(__GNUC__)
#    pragma GCC diagnostic pop
#endif
    }
 
    template <class T>
    constexpr auto buffer_view<T>::begin() -> iterator
    {
        return iterator(p_data);
    }
 
    template <class T>
    constexpr auto buffer_view<T>::end() -> iterator
    {
        return iterator(p_data + m_size);
    }
 
    template <class T>
    constexpr auto buffer_view<T>::begin() const -> const_iterator
    {
        return cbegin();
    }
 
    template <class T>
    constexpr auto buffer_view<T>::end() const -> const_iterator
    {
        return cend();
    }
 
    template <class T>
    constexpr auto buffer_view<T>::cbegin() const -> const_iterator
    {
        return const_iterator(p_data);
    }
 
    template <class T>
    constexpr auto buffer_view<T>::cend() const -> const_iterator
    {
        return const_iterator(p_data + m_size);
    }
 
    template <class T>
    constexpr auto buffer_view<T>::rbegin() -> reverse_iterator
    {
        return reverse_iterator(end());
    }
 
    template <class T>
    constexpr auto buffer_view<T>::rend() -> reverse_iterator
    {
        return reverse_iterator(begin());
    }
 
    template <class T>
    constexpr auto buffer_view<T>::rbegin() const -> const_reverse_iterator
    {
        return crbegin();
    }
 
    template <class T>
    constexpr auto buffer_view<T>::rend() const -> const_reverse_iterator
    {
        return crend();
    }
 
    template <class T>
    constexpr auto buffer_view<T>::crbegin() const -> const_reverse_iterator
    {
        return const_reverse_iterator(cend());
    }
 
    template <class T>
    constexpr auto buffer_view<T>::crend() const -> const_reverse_iterator
    {
        return const_reverse_iterator(cbegin());
    }
 
    template <class T>
    constexpr void buffer_view<T>::swap(buffer_view<T>& rhs) noexcept
    {
        std::swap(p_data, rhs.p_data);
        std::swap(m_size, rhs.m_size);
    }
 
    template <class T>
    constexpr buffer_view<T> buffer_view<T>::subrange(size_type pos, size_type count) const
    {
        SPARROW_ASSERT_TRUE(pos <= size());
        SPARROW_ASSERT_TRUE(count <= size() - pos);
        return buffer_view<T>(p_data + pos, count);
    }
 
    template <class T>
    constexpr buffer_view<T> buffer_view<T>::subrange(size_type pos) const
    {
        SPARROW_ASSERT_TRUE(pos <= size());
        return buffer_view<T>(p_data + pos, size() - pos);
    }
 
    template <class T>
    constexpr buffer_view<T> buffer_view<T>::subrange(const_iterator first, const_iterator last) const
    {
        SPARROW_ASSERT_TRUE(first >= begin() && last <= end());
        return buffer_view<T>(first, last);
    }
 
    template <class T>
    constexpr buffer_view<T>::operator buffer<std::remove_const_t<T>>() const
    {
        if (!p_data)
        {
            return buffer<std::remove_const_t<T>>();
        }
        else
        {
            return buffer<std::remove_const_t<T>>(cbegin(), cend());
        }
    }
 
    template <class T>
    bool operator==(const buffer_view<T>& lhs, const buffer_view<T>& rhs)
    {
        return lhs.size() == rhs.size() && std::equal(lhs.begin(), lhs.end(), rhs.begin());
    }
}